1. Field of the Invention
The object of the present invention are polymers of caprolactam, having high characteristics of impact resistance, containing a rubbery phase homogeneously distributed within the polymers themselves, obtained by means of the anionic polymerization, said rubbery phase consisting of alternating copolyesteramides of the type disclosed in U.S. Pat. No. 4,105,640, dated Aug. 8, 1978 and the related production process.
The process consists of dissolving or swelling the copolyesteramide elastomer inside monomer caprolactam, and submitting such mixture to the polymerization in the presence of a basic initiator, and then of an activator, at temperatures comprised within the range of from 120.degree. to 180.degree. C., optionally directly within the mold (according to the so called RIM, i.e., reaction injection moulding, method), thus obtaining the finished articles.
2. Description of the Prior Art
Polycaprolactam is, as it is well known, an important class of polyamides; it is a thermoplastic material having optimum mechanical and physical characteristics, which allow it to be used, in addition to the production of fibers, also for the production of technical articles.
It is not suitable, however, for the production of items of large dimensions, and for parts requiring a certain degree of flexibility and of impact strength, because of its fragility. Polymers of higher lactams, such as polylauryllactam, show a higher flexibility, and, due to their lower absorption of moisture, a higher dimension al stability. Their characteristics, however, are not such as to allow some uses, especially at low temperatures.
Some copolymers of caprolactam, obtained by anionic polymerization in the presence of new initiators, such as, e.g., copolymers with polyethers and/or polyesters (U.S. Pat. Nos. 3,993,709; 3,944,629; 3,682,262) have been proposed; they show a greater resilience together with a higher moisture absorption. They have, however, the disadvantage of a low thermal stability, which limits their use possibilities.